Aviation fuel blending agent



ZJUQ Q6 Filed OGM .'50, 1344 United States Patent rvce AVIATION FUEL BLENDING AGENT Herbert H. MeienBaytown, Tex., assignor to Esso Research and Engineering Company, a corporation of Delaware Application October 30, 1944, Serial No. 561,117

4 Claims. (Cl. Mtl-683.6)

The present invention is directed to a method of preparing an aviation fuel blending agent ot' high octane number. More particularly the invention is concerned with a separation method whereby triptane is obtained from a mixture of other hydrocarbons having 7 carbon atoms in the molecule.

Triptane is unique in being the only saturated compound of the paraftin series having 7 carbon atoms and containing 3 methyl groups as side chains. By virtue of the structural configuration of triptane, it has an exceedingly high octane number which makes it a very valuablecompound to be included in aviation fuel. Be cause triptane occurs in hydrocarbon mixtures containing other hydrocarbons Which boil very close to its boiling point, it is exceedingly diiiicult to make a separation to obtain the purified compound. When triptane is obtained by hydrogenation of oleinic mixtures containing the corresponding oleiins, the separation problem is multiplied due to the large number of isomers encountered.

lt is, therefore, the main object of the present inven tion to provide a method for separating triptane from other hydrocarbon compounds containing 7 carbon atoms. Another object of the present invention is to provide a method of obtaining from olenic mixtures a high octane number blending agent comprising triptane.

in carrying out the process of the present invention a mixture of C7 oletins and paraftins containing 2,3,3-trimethyl1butene is subjected to superfractionation to obtain a fraction boiling in the range from 70 to 80 C. which contains substantially all of the 2,3,3trimethyllbutene. There are two paraiiins having 7 carbon atoms besides triptane which boil very closely to the olefin corresponding to triptane. These two parainic conipounds would contaminate the triptane fraction it present, but in accordance with the practice of the present invention, Vthe presence ot these compounds causes no ditficulty.

As recorded in Physical Constants ot the Principal Hydrocarbons, 4th edition, compiled by M. i. Doss, the Cs and C7 oletins which boil close to 2,3,3-trimethyl- 1-bntene are as follows:

2,709,196 Patented May 24, 1955 laccording to the present invention, after obtaining a narrow boiling oletin-paratiin fraction. centered around the boiling point ot` 2,3,3-trimethyl-1butene, the next step is the separation of the oleiins, in which the double bonds are attached to the tertiary carbon atoms, from the parains and those oletins in which the double bond is not attached to a tertiary carbon atom. This may be accomplished by catalytically alkylating; the tertiary oletins with phenol or cresol by methods disclosed in the literature and then catalytically dealkylating the alkylated phenol to recover the tertiary olefin. The method of catalytcally dealkylating alkylated phenol also has been disciosed in the literature. By reference to the above tabulation it will be seen that three of the 7 carbon atom oiens (4,4-dimethyl-2pentene, 3,3-dimethyl-1f pentene, and 4,4-dirnethyl-1-pentene) do not have double bonds attached to tertiary carbon atoms whereas 2,3,3- trimethyl-1-butene, 2,4-dimethyl-2-pentene and 2,4- dimethyl-l-pentene, as well as 2,3-dimethyl-2-butene, which boil very Close to 2,3,3-trimeti1yl-l-butene, do have a double bond attached to the tertiary carbon atoms. Since the subsequent steps in the present invention include a hydrogenation step and since two of the aforementioned compounds, namely, 2,4-dimethyl-2-pentene and 2,4-dimethyl-l-pentene subsequently hydrogcnate to fi-dimethyl pentane which has a relatively low octane number and boils very close to triptane, it is desirable to fractionate the original cut so as to exclude these compounds. The boiling point spread between them and the olefin corresponding to triptane is of the order of 3.2" to 4.1 C. making this a. ditiicult but not impossible separation. The present invention lcontemplates exclusion of these two compounds either before conducting the aikylation and dealitylation operations or after these operations. It is advantageous to make the separation to exclude the undesirable compounds after the alkylation and dealitylation steps since the amount of material subjected to the very .high degree of fractionation is reduced. The presence of 2,3dimethyl-2-butene in the feed to the hydrogenation step of my invention offers little difficulty since it hydrogenates to the Very desirable 2,3-dimethyl butane which, because of its relatively high octane number, may be mixed advantageously with the trptane itself. it is contemplated, however, that the lli-dimethyl butano may be separated from the triptane in a subsequent fractionation step which can be easily accomplished by virture of the relatively large spread in the boiling points of triptane and 2,3-dimethyl butane.

After the tertiary oleiins have been recovered from the dealkylation step of the present invention, `theynare then ysubjected to hydrogenation and subsequent fractionation steps as may be desired.

The present invention will be further illustrated by reference to the drawing in which the single figure is in the form of a iiow plan of a preferred embodiment thereof. Referring now to the drawing, numeral 11 designates a line through which a C'z hydrocarbon fraction containing olefins and paraffins and which contains 2,3,3- trimethyl-l-butene is fed into a fractionation zone 12. It is understood that fractionation zone 12 may comprise a number of distillation towers equipped to allow sharp separation between compounds having close boiling points. In this particular instance fractionation zone 12 is illustrated as being a single tower and as provided with heat- -ing means 10. A fraction boiling below 70 C. is discharged by line 13 for further handling and a fraction boiling above 80 C. is discharged therefrom by way of line 14 while a side stream boiling between 70 and 80 C. is withdrawn by line 1S for handling in accordance with the present invention.

The narrow boiling hydrocarbon fraction discharged from zone 12 by line 15 is intermingled in line 16 with a phenolic compound introduced by line 17 and the mixed stream passes through incorporator or mixing device 18 for thorough mixing between the hydrocarbons and phenolic compound. The phenolic compound intermingled with the hydrocarbon stream carries a small quantity of a catalytic agent such as sulfuric acid, benzene sulphonic acid, toluene sulphonic acid, and other material which is introduced into line 17 by line 19 controlled by valve 20. The admixture of hydrocarbons, phenolic compound andV catalyst is discharged from the incorporator 18 by way of line 21 into an alkylation zone 22'where the tertiary olefins react with the phenolic material to form the corresponding tertiary alkyl phenol; the paraflins, primary and secondary oleiins pass outwardly from alkylation zone 22 by way of line 23.

The conditions obtaining in alkylation zone 22 have been well disclosed in the patent literature and further reference to them need not be made. Sutlice to say that the conditions in the zone 22 are adjusted to give substantially complete reaction between the tertiary olefins and the phenolic material.

The tertiary alkyl phenols pass from alkylation zone 22 into line 24 and discharge thereby into dealkylation zone 25 which is shown schematically and is provided with a heating means 26 for adjustment of temperature and pressure to allow recovery of the tertiary olefins from the alkylated phenol. As the conditions are adjusted in dealkylation zone 25, tertiary olens are released therefrom and are discharged overhead by way of line 27 while the released phenolic materials are discharged by line 17 and are recycled to treat additional hydrocarbons as has been described.

If the high boiling tertiary olens (2,4-dimethyl-2- t pentene and 2,4-dimethyl-l-pentene) had not been excluded from the stream withdrawn from fractionation zone 12 by line 15. it would be desirable to separate them from the recovered tertiary oleiins as pointed out before. In the event that the tertiary olelins discharged from dealkylation zone 25 by line 27 contain these undesirable tertiary oleiins, the recovered tertiary oleilns are routed from line 27 into line 28 controlled by valve 29 which introduce them into a second fractionation zone 30. Fractionation zone 30 includes facilities to make a sharp separation between 2,3,3-trimethyl-l-butene and the aforementioned higher boiling tertiary olefins and similar to fractionation zone 12 may comprise a plurality of fractionation towers. In this particular instance fractionation tower 30 has been illustrated with a single tower provided with a heating means 31 for adjustment of temperature and pressure. The high boiling tertiary olens boiling respectively at 82.0 and 81.1 C. are discharged from zone 30 by way of line 32 for further handling as may be desired while the 2,3,3-trimethyl-lbutene is recovered over-head by way of line 33 controlled by valve 34 and discharged thereby into hydrogenation zone 35 where conditions are adjusted to allow saturation of the tertiary olens. Hydrogenation zone 35 is provided with a line 36 for introduction of hydrogen thereto.

When the undesirable tertiary olens mentioned above are excluded from the hydrocarbon stream segregated in fractionation zone 12 and withdrawn by line 1S, it will be desirable to by-pass fractionation zone 30 entirely. This is accomplished by closing off valve 29 in line 28 and routing the recovered tertiary olens from dealkylation zone 25 through line 27 and into line 37 controlled by valve 3S and thereby into hydrogenation zone 35. Whether or not the higher boiling undesirable tertiary oleins were excluded in fractionation zone 12, essentially complete saturation of the hydrocarbons introduced into hydrogenation zone 35 is accomplished and the saturated material is discharged therefrom by way of line 39 and may be routed into a third fractionation zone 40. Similar to fractionation zones 12 and 30, fractionation zone 40 may comprise a plurality of fractionating towers but in the present embodiment is shown as a single tower provided with a heating means 50. The mixture of saturation hydrocarbons introduced by line 39 into zone 40 is subjected to super-fractionation to recover over-head by way of line 41 a fraction cornprising essentially 2,3-dimethyl butane and to recover as a side stream by line 42 a fraction consisting essentially of triptane. Any traces of heavy undesirable parafln hydrocarbons may be discharged from the zone 40 by line 43.

In some instances it may be undesirable to subject the stream issuing from hydrogenation zone 35 by line 39 to fractionation to separate the 2,3-dimethyl butane from the triptane since both of them have exceptionally high octane numbers and may be used together as an aviation blending agent. When fractionation zone 40 is not employed, valve 44 in line 39 is closed off and valve 45 in line 46 is opened allowing withdrawal of an aviation fuel blending agent thereby.

While the present invention has been described and illustrated by reference to separation of the tertiary olens corresponding to triptane from its mixtures with parafns and primary and secondary olens, it will be obvious to the skilled worker that the present invention may also be employed to separate triptane from its isomers in mixtures of the saturated hydrocarbons. rfhis may be accom plished by subjecting the mixtures of triptane and other hydrocarbons to a dehydrogenation step prior to charging the mixture to fractionation zone 12 of the preferred embodiment of the present invention.

The paraftins, primary and secondary olens discharged from the system by line 23 and the tertiary olens discharged by line 32 as well as the oleins and/or paraffins which are discarded by lines 13 and 14 lcontain valuable materials which may be employed in subsequent alkylation operations to prepare additional quantities of aviation fuel. It would be undesirable to subject these aforementioned fractions to hydrogenation since they convert on hydrogenation to material of relatively low octane number as compared to the relatively high octane number values of 2,3-dimethyl butane and triptane.

The present invention is not subject to employment in separating hydrocarbons having the 2,3,3 configuration other than 7 carbon atom hydrocarbons since the isomeric olelins of 8 and 9 carbon atoms, for example, are so numerous that it wouid be impossible to process them in accordance with the present invention. 'It may thus be seen that the series of processing steps in accordance with my invention is unique to the recovery of triptane from its mixtures with other 7 carbon atom-containing hydrocarbons.

The nature and objects of the present invention having been completely described and illustrated what I wish to claim as new and useful and to secure by Letters Patent l. A method for obtaining triptane from a mixture of olefmic hydrocarbons comprising the steps of fractionally distilling an olelinic mixture comprising C7 hydrocarbons and including 2,3,3-triniethyl-l-butene to obtain a fraction boiling between 70 and 80 C., alkylating the tertiary olens contained therein with a phenol and separating the alkylated phenol from the unreacted hydrocarbons, recovering tertiary olens from the alkylated phenol and hydrogenating the recovered tertiary olens to obtain a fraction rich in triptane.

2. A method for obtaining triptane comprising the steps of ractionally distilling a feed stock comprising C7 olefms and including 2,3,3-trimethyl-t-butene to obtain a fraction having a substantially' greater percentage of 2,3,3tri rnethyl1butene than the feed stock, alkylating tertiary olens contained in said fraction with phenol and sepa: rating the alkylated phenol from the unreacted hydrocarbons, recovering tertiary olens from the alkylated phenol and hydrogenating the recovered tertiary olens to obtain a fraction rich in triptane.

3. A method in accordance with claim 2 in which the fraction separated from the feed stock boils in the range of 70 `to 80 C.

4. A method for obtaining triptane comprising the steps of fractionally distilling a feed stock comprising C7 oleins and including 2,3,3trimethyl-lbutene to obtain a fraction boiling in the range of 70 to 80 C., alkylating the tertiary oleins in the fraction with a phenol, separating the resulting alkylated phenol from the unreacted hydrocarbons, recovering tertiary olens from the alkylated phenol, hydrogenating the recovered tertiary olens to obtain a product including triptane and distilling said product to separate a triptane-rich fraction therefrom.

References Cited in the tile of this patent UNITED STATES PATENTS 2,265,583 Stevens et al Dec. 9, 1941 2,360,253 Marschner n- Oct. 10, 1944 2.370.810 Morrell et al Mar. 6. 1945 

1. A METHOD FOR OBTAINING TRIPTANE FROM A MIXTURE OF OLEFINIC HYDROCARBONS COMPRISING THE STEPS OF FRACTIONALLY DISTILLING AN OLEFINIC MIXTURE COMPRISING C7 HYDROCARBONS AND INCLUDING 2,3,3-TRIMETHYL-1-BUTENE TO OBTAIN A FRACTION BOILING BETWEEN 70 AND 80* C., ALKYLATING THE TERTIARY OLEFINS CONTAINED THEREIN WITH A PHENOL AND SEPARATING THE ALKYLATED PHENOL FROM THE UNREACTED HYDROCARBONS, RECOVERING TERTIARY OLEFINS FROM THE ALKYLATED PHENOL AND HYDROGENATING THE RECOVERED TERTIARY OLEFINS TO OBTAIN A FRACTION RICH IN TRIPTANE. 